JPH08209276A - Alloy material for thixocasting - Google Patents

Abstract

(57) [Summary] [Object] To provide an Al alloy material capable of obtaining a sound casting under the application of the thixocasting method. [Constitution] In the differential thermal analysis curve c of the Al alloy material,
There are a first chevron endothermic part d formed by eutectic melting and a second chevron endothermic part e formed by melting a component having a melting point higher than the eutectic point.
When the peak temperature of the first chevron endothermic part d is T ₁ and the peak temperature of the second chevron endothermic part e is T ₂ , both peak temperatures T
The difference between ₁ and T ₂ is T ₂ −T ₁ is 20 ° C. ≦ T ₂ −T ₁ ≦ 80 ° C.
Is. Thereby, the primary crystal α-Al at the time of heating the material
Can be prevented to promote fine spheroidization and uniform dispersion of primary α-Al.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an alloy material used for carrying out a thixocasting method.

[0002]

2. Description of the Related Art Heretofore, as this kind of alloy material, in a differential thermal analysis curve, there exists a first chevron endotherm due to eutectic melting and a second chevron endotherm due to melting of a component having a melting point higher than the eutectic point and, the peak temperature of the first angled endothermic section and T _1, when the peak temperature of the second angled endothermic section was T _2, the difference T ₂ -T ₁ of both the peak temperature T _1, T ₂ is T ₂ -T
Alloy materials with ₁ <20 ° C are known.

In carrying out the thixocasting method, the alloy material is subjected to heat treatment to prepare a semi-molten alloy material in which a solid phase (a substantially solid phase, the same applies hereinafter) and a liquid phase coexist, Then, the semi-molten alloy material is filled into the cavity of the mold under pressure, and then the semi-molten alloy material is solidified under pressure.

As described above, the reason why the difference T ₂ -T ₁ between the two peak temperatures T ₁ and T ₂ is set small is that the solid-liquid coexisting temperature range of the alloy material is narrowed to suppress shrinkage cavities during solidification. Especially.

[0005]

However, the alloy material in which the difference T ₂ -T ₁ between the two peak temperatures T ₁ and T ₂ is set to a small value as described above has a solid phase ratio sensitive to changes in heating temperature. In order to uniformly heat the alloy material, the temperature rising rate must be decreased, that is, the heating time must be set longer, resulting in coarsening of the primary crystal, which is the main component of the solid phase. Will cause problems such as On the other hand, if the heating rate is increased, that is, if the heating time is set to be short, the solid fraction distribution in the semi-molten alloy material becomes non-uniform, so the semi-molten alloy material is injected into the cavity of the mold in the injection process. As a result, air is entrained in the semi-molten alloy material to generate relatively large pores, which causes a problem.

[0006] The present invention has been made in view of the above, first, by identifying the difference T ₂ -T ₁ of both the peak temperature T _1, T ₂ in the second angled endothermic section, has a sound casting quality, also good It is an object of the present invention to provide the alloy material for thixocasting, which enables to obtain a casting having high mechanical properties such as high fatigue strength.

[0007]

In the differential thermal analysis curve, the alloy material for thixocasting according to the present invention has a first chevron endothermic part due to eutectic melting and a first chevron endothermic part due to melting of a component having a melting point higher than the eutectic point. There are two chevron-shaped endotherms, and the first
Assuming that the peak temperature of the mountain endothermic part is T ₁ and the peak temperature of the second mountain endothermic part is T ₂ , both peak temperatures T ₁ ,
Wherein the difference T ₂ -T ₁ of T ₂ is _{20 ℃ ≦ T 2 -T 1 ≦} 80 ℃.

[0008]

In the alloy material in which the difference T ₂ -T ₁ between the two peak temperatures T ₁ and T ₂ is specified as described above, the fluctuation of the solid fraction with respect to the heating temperature change is slowed down. Can be raised to heat the alloy material to the casting temperature (the temperature of the material at the time of casting) in a short time, whereby coarsening of the primary crystal is prevented.

Further, as the solid-liquid coexisting temperature range is expanded, the diffusion of the primary crystal is actively carried out, so that fine spheroidization and uniform dispersion of the primary crystal are promoted. This leads to a homogenization of the structure in the semi-molten alloy material, so that a homogeneous solidification of the material is achieved, whereby the occurrence of shrinkage cavities is avoided.

However, the difference between the two peak temperatures T ₂ −T ₁ is T
₂ -T ₁ <occurs a problem such as the above at 20 ° C., whereas, T ₂ -T _1> shrinkage cavities easily occur at the time of solidification because the solid-liquid coexisting temperature range of 80 ° C. The alloy material is too wide .

[0011]

EXAMPLE A pressure casting machine 1 shown in FIG. 1 uses an Al alloy material (alloy material) under the application of the thixocasting method.
l Used for casting alloy castings. The pressure casting machine 1 includes a fixed mold 2 and a movable mold 3 having vertical mating surfaces 2a and 3a, and a casting molding cavity 4 is formed between the mating surfaces 2a and 3a. Semi-molten in fixed mold 2
A chamber 6 in which the 1-alloy material 5 is installed is formed, and the chamber 6 communicates with the cavity 4 via a gate 7.
Further, a sleeve 8 communicating with the chamber 6 is horizontally attached to the fixed mold 2, and a pressure plunger 9 inserted into and removed from the chamber 6 is slidably fitted to the sleeve 8. The sleeve 8 has a material insertion port 10 in the upper portion of the peripheral wall thereof.

Table 1 shows the compositions of Examples A to G of Al alloy materials and Comparative Examples a and b. Example A is Al-Si-
Cu-based alloy, Examples B to D are Al-Si-Mg-based alloys,
Examples E to G and Comparative Example a are Al-Cu based alloys, and Comparative Example b is Al-Zn-Mg based alloy. These Examples A
Etc. were cut from a high-quality long continuous casting material cast under the application of the continuous casting method, and in the casting, spheroidizing treatment of primary crystal α-Al was performed. There is. The dimensions of Example A and the like are 50 mm in diameter and 65 mm in length.

[0013]

[Table 1] When the differential scanning calorimetry (DSC) was performed on Example A, the results shown in FIG. 2 were obtained. The differential thermal analysis curve c has a first chevron endothermic part d due to eutectic melting and a second chevron endothermic part e due to melting of a component having a melting point higher than the eutectic point. In this case, the peak temperature T ₁ of the first chevron endothermic part d is T
₁ = 559 ° C., the peak temperature T ₂ of the second chevron endothermic part e is T
₂ = 579 ° C., and therefore both peak temperatures T ₁ , T
The difference T ₂ -T ₁ of ₂ was found to be T ₂ -T ₁ = 20 ℃.

Next, Example A is installed in the heating coil of the induction heating apparatus, and then the frequency is 1 kHz and the maximum output is 3.
Heating was performed under the conditions of 0 kW and a heating time of 7 minutes to prepare Example A in a semi-molten state in which a solid phase and a liquid phase coexist. In this case, the solid phase ratio is set to 40% or more and 60% or less.

Thereafter, as shown in FIG. 1, the semi-molten Example A (reference numeral 5) was placed in the chamber 6, and the casting temperature was changed.
572 ° C, moving speed of pressure plunger 9 0.2 m / se
c, Mold temperature The pressure was applied to Example A while passing through the gate 7 to fill the inside of the cavity 4. Then, by holding the pressure plunger 9 at the end of the stroke, a pressure is applied to the example A filled in the cavity 4, and the example A is solidified under the pressure to obtain an Al alloy casting A.

Further, DSC was performed on Examples B to G and Comparative Examples a and b, and the same casting operation as described above was performed using Example B and the like, and eight kinds of Al alloy castings B corresponding to Example B and the like were obtained. ~ G, a, b were obtained. In this case, the heating time is 7 minutes as described above, but for comparison, Comparative Example a is used and the heating time by the electric resistance furnace is set to 20 minutes.
l alloy casting a ₁ was obtained.

Next, each Al alloy casting A to G, a, a ₁ , b
Was subjected to T6 treatment under the conditions shown in Table 2.

[0018]

[Table 2] In order to perform a fatigue test, the Al alloy casting A after T6 treatment
From G, a, a ₁ and b, 8 test pieces having a parallel portion having a diameter of 4 mm and a length of 20 mm were produced for each of the Al alloy castings A to G, a, a ₁ and b. These test pieces were tested at different stress amplitudes at room temperature using an electrohydraulic fatigue tester to determine the number of cycles until failure. Then, the fatigue strength S ₁ at the number of repetitions of 10 ⁷ was obtained from these data.

3 to 8 and FIGS. 9 and 10 show Examples B to G.
And the differential thermal analysis curve a regarding Comparative Examples a and b is shown.

Table 3 shows Examples A to G and Comparative Examples a and b.
The peak temperatures T ₁ and T ₂ of the first and second chevron endothermic parts d and e, the difference T ₂ −T ₁ between the two peak temperatures T ₁ and T ₂ ,
Heating time and casting temperature and Al alloy castings A to G,
The presence / absence of voids, presence / absence of coarsening of primary α-Al, and fatigue strength S ₁ are shown for a, a ₁ and b, respectively.

[0021]

[Table 3] FIG. 11 is a micrograph showing the metal structure of the Al alloy casting G. 12 (a), 13 and 14 show Al
Alloy casting a, a micrograph showing a _1, b of the metal structure.

As is clear from FIGS. 2 to 8 and 11 and Table 3, in the Al alloy castings A to G, the difference between the two peak temperatures T ₂ −.
T ₁ was obtained using Examples A to G specified in the range of 20 ° C. ≦ T ₂ −T ₁ ≦ 80 ° C., and Examples A to G were obtained.
In G, since the fluctuation of the solid fraction with respect to the heating temperature change is slowed down, it is possible to increase the heating rate and heat Examples A to G to the casting temperature within a short time such as 7 minutes. Therefore, coarsening of the primary crystal α-Al is prevented by this.

With the expansion of the solid-liquid coexisting temperature range, the primary crystal α
-Al diffusion is actively performed, so that the primary crystal α-Al
The fine spheroidization and uniform dispersion of the above are promoted, and the occurrence of shrinkage cavities is also avoided.

From the above, the Al alloy castings A to G have sound casting quality and excellent fatigue strength.

In the case of the Al alloy casting a shown in FIG. 12, the difference T ₂ -T between both peak temperatures T ₁ and T ₂ in the comparative example a.
_{Since 1} is T ₂ −T ₁ <20 ° C., and the heating time is short such as 7 minutes, voids are generated due to the entrainment of air that occurs during cavity injection.

In the case of the Al alloy casting a ₁ shown in FIG. 13, the heating time of the comparative example a is as long as 20 minutes, so that the primary crystal α-Al (lump portion) becomes coarse.

In the case of the Al alloy casting b shown in FIG. 14, the difference T ₂ −T ₁ between the two peak temperatures T ₁ and T ₂ is T ₂ −T ₁ > 80.
Since the temperature was ℃, shrinkage cavities, and therefore voids (black portions) were generated during solidification.

For comparison, using Examples A to G and Comparative Examples a and b, conditions of extrusion temperature 350 to 420 ° C., container temperature 300 ° C., die temperature 250 ° C., die hole diameter 35 mm, extrusion ratio 4.7. Extrusion processing is performed by using Al alloy extruded materials A to G corresponding to Example A and the like,
a and b were obtained.

These Al alloy extruded materials A to G, a, b
Is subjected to T6 treatment (see Table 2) under the same conditions as those for the corresponding Al alloy castings A to G, a, b.
Then, a test piece similar to the above was prepared from the Al alloy extruded material A and the like, and a fatigue test similar to the above was performed to determine the fatigue strength S ₂ at the number of repetitions of 10 ⁷ .

Table 4 shows each Al alloy extruded material A to G, a,
fatigue strength S _{2 of} b and Al alloy castings A to G, a,
The strength ratio S ₁ / S ₂ between the fatigue strength S ₁ of a ₁ and b is shown.
In the table, the Al alloy extruded material a ₁ is the same as the a.

[0031]

[Table 4] FIG. 15 shows the difference T ₂ −T ₁ between the peak temperatures T ₁ and T ₂ in Examples A to G and Comparative Examples a and b and the intensity ratio S _1.
This is a graph of the relationship with / S ₂ . Point A in the figure
-G and points a and b are examples A to G and comparative examples a and b.
Is applicable when is used. Point a ₁ is the case where the heating time in Comparative Example a is 20 minutes.

As is clear from FIG. 15 and Table 4, by using Examples A to G, it is possible to obtain Al alloy castings A to G having the same fatigue strength as the Al alloy extruded materials A to G. . This also difference T ₂ of the two peak temperatures T _1, T ₂
-T ₁ to understood that it may be set to _{20 ℃ ≦ T 2 -T 1 ≦} 80 ℃.

The alloy material according to the present invention is not limited to the Al alloy material.

[0034]

According to the present invention, by providing the above-mentioned thermal characteristics, under the application of the thixocasting method, the casting quality is sound and the fatigue strength is excellent. It is possible to provide an alloy material capable of obtaining a casting having high mechanical properties.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a pressure casting machine.

2 is a main part of a differential thermal analysis curve of Example A. FIG.

FIG. 3 is a main part of a differential thermal analysis curve of Example B.

FIG. 4 is a main part of a differential thermal analysis curve of Example C.

5 is a main part of a differential thermal analysis curve of Example D. FIG.

6 is a main part of a differential thermal analysis curve of Example E. FIG.

FIG. 7 is a main part of a differential thermal analysis curve of Example F.

8 is a main part of a differential thermal analysis curve of Example G. FIG.

FIG. 9 is a main part of a differential thermal analysis curve of Comparative Example a.

FIG. 10 is a main part of a differential thermal analysis curve of Comparative Example b.

FIG. 11 is a micrograph showing the metal structure of an Al alloy casting G.

FIG. 12 (a) is a micrograph showing the metal structure of an Al alloy casting a, and FIG. 12 (b) is a principal part map of FIG.

FIG. 13 is a micrograph showing the metal structure of an Al alloy casting a ₁ .

FIG. 14 is a micrograph showing a metal structure of an Al alloy casting b.

FIG. 15 is a difference T ₂ −T ₁ between both peak temperatures and an intensity ratio S ₁ /
Is a graph showing the relationship between S _2.

[Explanation of symbols]

c Differential thermal analysis curve d First chevron endotherm e Second chevron endotherm T ₁ , T ₂ peak temperature

[Procedure amendment]

[Submission date] February 20, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

3 to 8 and FIGS. 9 and 10 show Examples B to G.
3 shows a differential thermal analysis curve c for Comparative Examples a and b.

Claims (1)

[Claims] 1. In a differential thermal analysis curve (c), a first chevron endotherm (d) due to eutectic melting and a second chevron endotherm (e) due to melting of a component having a melting point higher than the eutectic point Exists,
The first angled endothermic section peak temperature of (d) and T _1, when said second angled endothermic section peak temperature of (e) was T _2, both the peak temperature T _1, the difference between T ₂ T ₂ -T ₁ is 20 ° C ≤
Thixocasting alloy material characterized by a T ₂ -T ₁ ≦ 80 ℃.